This invention is directed to safety feature for a function control circuit and in particular to a safety circuit for a function control circuit particularly adapted for use with a timing circuit adapted to produce a time based signal to prevent erroneous function control thereof.
Although function control circuits controlled by manually operated switches disposed on the exterior of a device have taken on various forms, heretofor such function control devices have been particularly susceptible to inadvertent function selection caused by the use of a single manually operated switch to select more than one function. For example, in an electronic timepiece, the control of different functions such as time correction and alarm control are effected by a single manually operated switch selecting a first function in response to a pulling of same and a second function in response to a pushing of same. Inadvertent and erroneous function selection is also effected by rotatable switches adapted to effect selection of a first function in response to a rotation of the switch in a first rotational direction and selection of a second function in response to rotation in an opposite rotational direction.
The inadvertent and erroneous selection of an incorrect function in electronic timepieces has become particularly troublesome as the emphasis in electronic wristwatches has shifted from the mechanical display wristwatches wherein a hand or a disc is utilized to effect display to digital display wristwatches wherein a conventional seven-bar display formed of liquid crystals or light emitting diodes is utilized. By utilizing a quartz crystal oscillator circuit as a time standard and C-MOS integrated circuitry for producing low frequency time signals to be applied to the digital display elements, a highly accurate and small sized electronic wristwatch can be provided. Moreover, such diverse functions as chronography, alarms, the ability to instantaneously provide timing information corresponding to different time zones, and calculators have been included in such electronic wristwatches. Nevertheless, as the number of different functions and operations in electronic wristwatches have increased, so too has the number of manually operated switches required to effect same.
For example, in a chronographic wristwatch, a first switch means is required for effecting a selection of either a timekeeping mode of operation or an elapsed time measurement mode of operation. Additionally, a further switch is required for selecting the digit of time to be corrected (date, day, hour, minute, second, etc.), and still a further switch is required to control the elapsed time measurement functions found in a chronographic timepiece.
Nevertheless, because the fewest possible number of manually operated switches is a desired expedient for providing for simplicity of design and for maintaining the electronic wristwatch watertight, each switch or button is selected to perform as many functions as possible.
Specifically, a multi-position switch is pushed in and pulled out, or is rotated in a first or second direction in order to provide a selection of two different functions or operations by a single switch. Nevertheless, because of the small size of the switch, and the minimum displacement thereof to effect such function selection, inadvertent and erroneous selection of functions often results. Accordingly, a safety feature in a function control circuit to prevent inadvertent and erroneous function selection in response to manual operation of a multi-position switch is desired.